During the early part of the forthcoming year (1974) it is planned to complete the skeletonization of our collection of 274 monkeys (Macaca mulatta), which number includes both sexes and ranges in age from approximately the middle of the gestation period (164-180 days) to 13 or more years of age. The gravimetric weights of these skeletons (the weight of 20 subdivisions and of the total of each skeleton) will be determined and the pattern of increase in weight with age will be compared between the sexes and with that found for human skeletons. It is planned, also, to measure in 1974 the volumes of the long limb bones (humeri, radii, femora and tibiae) as a step in determining the density (weight/volume) and its pattern of development with age. The pattern will be compared with that found in human skeletons. The difficulties in obtaining a well distributed series of young monkey skeletons are considerably less than for young human skeletons, and it is expected that the findings on the monkey will clarify through better definition the pattern of development of skeletal weight and bone density found in children's skeletons.